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Updated: Jan 26, 2026

Supercritical Nitrogen Processing for the Purification of Reactive Porous Materials
Published on: May 15, 2015
Improved Processability and the Processing-Structure-Properties Relationship of Ultra-High Molecular Weight
Galip Yilmaz1,2, Thomas Ellingham3,4, Lih-Sheng Turng5,6
1Polymer Engineering Center, Department of Mechanical Engineering, University of Wisconsin⁻Madison, Madison, WI 53706, USA. gyilmaz@wisc.edu.
Abstract:
The processability of injection molding ultra-high molecular weight polyethylene (UHMWPE) was improved by introducing supercritical nitrogen (scN₂) or supercritical carbon dioxide (scCO₂) into the polymer melt, which decreased its viscosity and injection pressure while reducing the risk of degradation. When using the special full-shot option of microcellular injection molding (MIM), it was found that the required injection pressure decreased by up to 30% and 35% when scCO₂ and scN₂ were used, respectively. The mechanical properties in terms of tensile strength, Young's modulus, and elongation-at-break of the supercritical fluid (SCF)-loaded samples were examined. The thermal and rheological properties of regular and SCF-loaded samples were analyzed using differential scanning calorimetry (DSC) and parallel-plate rheometry, respectively. The results showed that the temperature dependence of UHMWPE was very low, suggesting that increasing the processing temperature is not a viable method for reducing injection pressure or improving processability. Moreover, the use of scN₂ and scCO₂ with UHMWPE and MIM retained the high molecular weight, and thus the mechanical properties, of the polymer, while regular injection molding led to signs of degradation.
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